CodeSOD: AAYFN

Jason M sends us some Ruby code.

def bv(prop, tv="Yes", fv="No", nv="Not Specified") v = self.send(prop) if v === true tv elsif v === false fv else nv end end

The obvious WTF here is the function name and parameter names. AAYFN(always abbreviate your function names) seems to be the convention here. But it also contains a more Ruby-specific WTF.

The function name bv is short for "boolean value", obviously. tv is the "true value", fv is the false value, and nv is the null value. So this is really about pretty-printing boolean values and converting them to strings. While the terrible names make it hard to understand, it's not that hard to figure out what's going wrong here. I hate it, don't get me wrong, but it just makes me sigh with disappointment, not groan.

No, the thing that makes me groan is v = self.send(prop). This is a very Ruby idiom that lets you access a member of the class by name; essentially it's like doing self.prop, but since prop is a variable containing a property name, we have to send it.

This is metaprogramming by strings, which is the main reason I end up hating it. But in this specific instance, it offers us a lot of potential issues. First, if prop is anything not boolean, we just return "Not Specified", which is incredibly misleading. I'd argue that if we attempt to use it on a non-boolean field we should throw an exception. Which opens the question: if prop doesn't exist, is that a non-boolean field, or is that a "enh, just call it null" situation? Because right now, that will throw an exception. It'll also throw an exception if the thing being accessed is a function that takes parameters. These behaviors may be surprising.

Now, I don't know the calling pattern. It's possible that whatever function calls this already has a good list of the allowed boolean values, and will never call this on a prop that doesn't exist. Certainly, that's what the Ruby docs recommend. But I'm going to hate it anyway, because this kind of runtime metaprogramming by passing strings around is eternally asking for trouble. And while I haven't done a huge amount of Ruby, I've done enough to know that any non-trivial codebase ends up like this once the metaprogramming band-aid is taken off.

Now, if you don't mind, I'll go back to doing my metaprogramming with C++ templates, which are simple, clear, and never result in wildly unmaintainable code because you ended up reimplementing LISP in template operations.

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